This disclosure generally relates to monitoring of hydrocarbon wellbores. In particular, this disclosure relates to systems and methods for monitoring a wellbore using Distributed Acoustic Sensing (DAS).
When performing subterranean operations, acoustic sensing may be used to measure many important properties and conditions of a wellbore, pipeline, other conduit/tube, or fluids used. For example, when performing subterranean operations, it may be desirable to monitor a number of properties related to the subterranean formation and/or conduits used downhole, including, but not limited to, pressure, temperature, porosity, permeability, density, mineral content, electrical conductivity, and bed thickness. Further, certain properties of fluids used in conjunction with performance of subterranean operations, such as pressure, temperature, density, viscosity, chemical elements, and the content of oil, water, and/or gas, may also be important measurements. In addition, downhole-logging tools based on sonic well logging systems may be used to measure downhole properties such as formation porosity, location of bed boundaries and fluid interfaces, well casing condition, and behind casing cement location and bonding quality. Monitoring properties and conditions over time may have significant value during exploration and production activities.
A DAS system may be capable of producing the functional equivalent of 10 s, 100 s, or even 1000 s of acoustic sensors. Properties of downhole formations surrounding or otherwise adjacent to a wellbore may be monitored over time based on the acoustic sensing. Further, hydrocarbon production may be controlled, or reservoirs may be managed based on the downhole formation properties sensed by in-well acoustic measurement methods using a DAS system.
Acoustic sensing based on DAS may use the Rayleigh backscatter property of a fiber's optical core and may spatially detect disturbances that are distributed along the fiber length. Such systems may rely on detecting phase changes brought about by changes in strain along the fiber's core. Externally-generated acoustic disturbances may create very small strain changes to optical fibers. The acoustic disturbance may also be reduced or masked by a cable in which the fiber is deployed.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.